The present invention relates to a water-inseparable concrete composition a concrete constitutent whereof is not separated or washed away in water and containing a proper proportion of an admixture capable of imparting viscosity to the cement, which does not become separated from an aggregate which is embedded therein to form concrete, and which has a strength comparable to or higher than that of a viscous cement containing no such admixture.
As concrete is being laid under water, the cement may become separated or washed away from a part of the aggregate upon contact with the water, either as the concrete mix is falling through the water or as the concrete mix is spreading in a widthwise direction under water. The part of the concrete mix from which the cement has been separated or washed away subsequently deteriorates. In order to prevent the cement from becoming separated from the concrete mix in water, a viscosity building agent or viscosity builder such as an acrylic polymer compound, a cellulose derivative or the like may be included in an amount ranging from about 2% to about 4% by weight based on the cement content of the mix. However, a concrete mix containing such a polymer viscosity builder tends to have a delayed setting time and to have a lower strength, particularly initially, than a concrete mix containing no such agent. This tendency becomes more pronounced as the amount of the viscosity builder is increased. These drawbacks are the biggest obstacle in improving the performance of concrete laid under water by the use of a viscosity builder.